Coaxial thermistor mount



April 1954 D. w. BOWERS, JR, ET AL 2,677,109

COAXIAL THERMISTOR MOUNT Filed May 1, 1946 IN V EN TORS DANA W. BOWERS, J R

By RUDOLPH N.GR|ESHE|MER Wag/9&

ATTORNEY Patented Apr. 27, 1954 COAXIAL THERMISTOR MOUNT Dana W. Bowers, Jr., Cambridge, and Rudolph N. Griesheimer, Belmont, Mass., assignors, by mesne assignments, to the United States of America as represented by the Secretary of UNITED STATES PATENT OFFICE the Navy Application May 1, 1946, Serial No. 666,222

6 Claims. 1

circuit.

of Fig. 1.

conductor I I.

band type.

a smaller diameter.

in a temperature sensitive resistor, known as a thermistor, and measuring the resulting change I9 in place. Block in resistance by means of a Wheatstone bridge cap 2! by a washer 22 of insulating material The thermistor is frequently mounted and from body =I4 by the insulating cylinder I8. as the termination of a coaxial transmission line The connections of thermistor [5 are shown conducting the energy to be measured. Several in detail in Fig. 2. In the tapered end of inner problems arise in mounting a thermistor for this conductor II is a small diameter hole 24. Hole purpose. The mounting must present the proper 24 is slightly smaller in diameter than the wire terminating impedance over a broad frequency leads of thermistor I5. Longitudinal slots 25 are range so that reasonably small changes in frecut through the tapered end of inner conductor quency of the radio frequency energy will not af- II forming .a series of fingers. feet the impedance match. The mounting should of thermistor I5 is fitted into hole 24 being firmly also be simple with few adjustments and provide held by and in electrical contact with the fingers reliable electrical contact to the thermistor. formed in the end of inner conductor II.

The object of this invention is to provide a other wire lead of thermistor I5 passes through thermistor mounting for coaxial transmission 25 a small hole concentrically located in contact lines having the above features. plate I6 and ends in a like hole in backing block Other objects and advantages will be evident I9. This hole is slightly larger in diameter than from the following specification when taken with the Wire lead. On the face of contact plate I6 the accompanying drawings in which: next to block -I9 is a conical boss 26 concen- Fig. 1 is a sectional view of the invention, 30 trically located. On the face of block I9 next to Fig. 2 is an enlarged sectional view of a part plate I6 is a conical opening 21 leading to the small hole through block I9. The angle of the Referring now to Fig. 1 a section of coaxial conical boss 26 is greater than the angle of the transmission line is shown formed by a hollow conical opening 21 so that the boss 26 will not cylindrical outer conductor I0 and a round inner completely enter opening 21. Referring to Fig. l,

The coaxial line is provided with when end cap 2| is threaded onto body I4, presa coupling I2 to the source of electromagnetic sure is transmitted by insulating washer 22 to energy. The coupling I2 maybe any conventional block I9 forcing it toward plate I6.

design, the one shown is only for illustration. The is prevented from moving by mica disc I! and inner conductor II is supported by a short cirbody It. Thus, opening 21 is forced onto boss cuited stub support I3 of a conventional broad 26 creating a radially inward pressure on boss A. mounting body I4 of conductive 26. As plate I6 and boss 26 are of soft material,

material is mechanically fastened to the outer this pressure causes the hole through boss 26 conductor ID. A circular hole through body I4 to become smaller and the wire lead of thermistor forms an extension of the outer conductor I0 at I5 is firmly held and electrical contact is made between the wire lead and plate I6.

Inner conductor II ends at the opening of the In operation, the coaxial line is coupled to the hole through body I4. The inner conductor II source of radio frequency energy to be measured tapers to a small diameter at its end, the taper by coupling i2. extending a distance of approximately one-half completed through the inner conductor II, therwavelength from the end. Thermistor I5 is mistor I5, plate I6, the capacity between plate mounted to form an extension of inner conduc- I6 and body I4, body I4, and the outer conductor II through the hole in body I4. The wire tor ID. The capacity between plate I6 and body leads of thermistor I5 make contact at one end M across mica disc I1 is large enough to form to inner conductor II and at the other end to 2 contact plate I6. The details of these connections will be discussed later. Contact Plate I6 is a circular plate of soft conductive metal, preferably soft copper, and is insulated from body I4 by a mica disc I! and an insulating cylinder I8. Backing block I9, a circular plate of conductive material, makes contact to plate I6 and provides an external connection through terminal post 26. End cap 2I threads onto the outside diameter of body I4 and holds plate I6 and block I9 is insulated from end One wire lead The Plate 1 6 The radio frequency circuit is an effective short circuit for the radio frequency energy. The thermistor I presents both a resistive and inductive impedance. The effect of the reduced diameter of outer conductor formed by the hole in body I4 is to increase the capacity of the line at this point. This increased capacity cancels the inductive impedance of the thermistor 15. As the thermistor I5 is in series with the inner conductor, the resistance of the thermistor l 5 is high enough to form a very low Q termination of the line. Thus, the terminating impedance does not vary greatly over a wide frequency range. The taper of the inner conductor l l acts as an impedance matching section so that the coaxial transmission line is efiectively terminated in the proper impedance.

To provide a measurement of the effect of the radio frequency energy on thermistor G5, a resistance bridge, such as a Wheatstone bridge, is generally connected to measure the resistance change of thermistor I-E. This would require a direct circuit connection to thermistor 15. The direct current path is completed through the terminal 2G, block l9, plate Hi, the thermistor l5, inner conductor H, shorted stub I3, and the outer conductor ll The novel features of this thermistor mounting are: the broad banding obtained by the constricted outer conductor in the region of the thermistor, the mounting of the thermistor in series with the inner conductor, and the method of making secure contact to the thermistor. It is to be understood that the invention is not to be limited to the details of operation and construction shown in the accompanying drawing and described above, except as appears here after in the claims.

What is claimed is:

l. A broadband thermistor mounting for measurement of radio frequency power comprising, a section of coaxial transmission line having a tubular outer conductor and a cylindrical inner conductor, means for coupling radio frequency power to said coaxial line, a mounting body of conductive material, said mounting body terminating said outer conductor and having a cylindrical opening passing through it concentric with said coaxial line, said inner conductor ending at a point even with said opening in said mounting body, a small diameter cylindrical opening and a plurality of longitudinal slots in the end of said inner conductor, a thermistor having a first and second wire lead, said thermistor coaxially mounted in said opening in said mounting body, said first wire lead extending into said opening in said inner conductor and making electrical contact thereto, a circular plate of a conductive material, said plate having a small diameter hole through its center and on one face a conical boss concentric with said hole, a cylindrical block of conductive material having a conical opening concentrically located on one face, said circular plate fitting against said mounting body and being insulated therefrom, said second thermistor lead passing through said hole in said circular plate, said cylindrical block mounted concentric with said circular plate with said conical boss entering said conical opening, means for forcing said cylindrical block against said plate causing said conical boss to make contact with said second thermistor lead, means for insulating said circular plate and cylindrical block from said mounting body, and a means for providing electrical contact to said circular plate and cylindrical block.

2. A broadband thermistor mounting for measurement of radio frequency power comprising, a

section of coaxial transmission line having a tubular outer conductor and a cylindrical inner conductor, means for coupling radio frequency power to said coaxial line, a shorted stub support supporting said inner conductor coaxially with said outer conductor, said stub support providing a conductive connection from said inner conductor to said outer conductor, a mounting body of conductive material, said mounting body terminating said outer conductor and being mechanically and electrically fastened thereto, said mounting body having the form of a short cylinder with the end faces parallel and at right angles to the axis and having a cylindrical opening passing through it concentric with the axis, said inner conductor tapering to a, smaller diameter and ending at a point even with said opening in said mounting body, said taper extending substantially one half wavelength along said inner conductor, a small diameter cylindrical opening and a plurality of longitudinal slots in the end of said inner conductor, a circular plate of conductive material, said plate having a small diameter circular hole through its center and on one face a conical boss concentric with said hole, a mica disc having a concentric opening, a cylindrical conducting backing block having a concentric conical opening in one face, said circular plate fitting against said mounting body and being separated therefrom by said mica discs, said backing block mounted concentric with said circular plate with said conical boss of said circular plate entering said conical opening of said backing block, a thermistor having a first and second wire lead, said thermistor coaxially mounted in said opening in said mounting body being supported by said wire leads, said first wire lead extending into said opening in said inner conductor and making electrical contact thereto, said second lead extending through said hole in said circular plate, means for holding said mica disc, circular plate and backing block concentric with said coaxial line and forcing said backing block against said circular plate causing said conical boss in said plate to make electrical contact to said second wire lead of said thermistor, means for insulating said circular plate and backing block from said mounting block, and a terminal post providing an external connection to said backing block.

3. A broad band thermistor mount for measurement of ultra high frequency power comprising, a thermistor having first and second wire leads and presenting resistive and inductive impedance, a section of coaxial transmission line having outer and inner conductors, one end of said inner conductor being adapted to receive said first lead whereby said thermistor forms an extension of said inner conductor, a section of conductive material mounted in capacitive relationship to said outer conductor and terminating said transmission line by being conductively connected to said inner conductor through said second thermistor lead, said outer conductor being constricted in the vicinity of said thermistor for increasing the capacity of the line at that point by an amount sufiicient to resonate said inductive impedance of said thermistor whereby said thermistor presents substantially a purely resistive termination to said coaxial line, and said inner conductor being tapered at said lead-receiving end for matching said resistive termination to said coaxial line.

4. A thermistor mount as defined by claim 3 wherein said taper extends a distance of approximately one-half the Wave length of said ultrahigh frequency energy.

5. A broad band thermistor mount for measurement of ultra high frequency power comprising, a thermistor having first and second wire leads and presenting resistive and inductive impedance, a section of coaxial transmission line having an outer and inner conductor, one end of said inner conductor being adapted to receive said first lead of said thermistor whereby said thermistor forms an extension of said inner conductor, a clamp for electrically and mechanically coupling said second lead of said thermistor to an external circuit, said clamp comprising first and second conductive elements mounted within said outer conductor, said first conductive element having a hole in axial alignment with said inner conductor and a conical boss concentric with said hole, said second element having a conical hole in axial alignment with said inner conductor for receiving said boss, said second lead extending through said holes, means for urging said elements together whereby said boss is radially compressed to securely contact said lead, means for mounting said clamp in capacitive relationship with the end of said outer conductor, said outer conductor being constricted in diameter a predetermined amount at the location of said thermistor to increase the capacity of the line at that point to the value necessary to achieve series resonance with the in- References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,273,547 Radinger Feb. 17, 1942 2,399,674 Harrison May 7, 1946 2,407,075 Gurewitsch Sept. 3, 1946 2,411,553 Ramo Nov. 26, 1946 2,434,610 Feiker Jan. 13, 1948 2,437,482 Salisbury May 9, 1948 2,438,915 Hansen Apr. 6, 1948 2,446,982 Pound Aug. 10, 1948 2,473,495 Webber June 14, 1949 2,525,901 Hansen et a1 Oct. 17, 1950 2,590,477 Weber Mar. 25, 1952 OTHER REFERENCES Coaxial-Line Discontinuities, by Whinnery et al., published in Proceedings of the I. R. E., volume 32, No. 11, November, 1944, pp. 695-709. 

